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The advantages of this piggyback approach to creating vaccines are enormous. First, there is no risk of actually getting herpes, hepatitis B or influenza from the injection, since the viruses themselves are not present in the formula. Second, the smallpox vaccine, however it is altered, is cheap, easy to use and does not require refrigeration—all tremendous advantages in Third World countries, where infectious diseases are rampant. "It would cost about 300 a shot, and only one shot would be required," says Molecular Virologist Geoffrey Smith of the NIAID team. By contrast, an injection of a hepatitis-B vaccine currently costs $100, and two or three doses are necessary.
Perhaps the greatest advantage of the new method is the possibility of creating a single vaccine that would be effective against a dozen or more different diseases. The cowpox virus is so large, says Paoletti, that "there is enough room to insert twelve to 15 different foreign genes. We could perhaps develop a polyvaccine that would render a person immune to herpes, hepatitis, malaria and other diseases, all in one shot."
But Paoletti believes that it will be at least three years before the vaccines can be tested on humans and several more before they can be marketed. In addition, he notes, there is no evidence that the herpes vaccine will help the 20 million Americans who already have the disease. "I think there is no question that this is a potential method of prophylaxis, but we cannot yet speak to the question of cure."
Other scientists have much graver doubts about the health department's work. "While this represents an elegant piece of genetic engineering, I have some reservations about the safety of using vaccinia," warns Virologist Edwin D. Kilbourrie, of Mount Sinai Hospital in New York City. "The risks are remote and rare," says Pediatric Immunologist Vincent Fulginiti of the University of Arizona, but he agrees with Kilbourne. The danger: vaccinia can be transferred by contact from the site of inoculation to the eye, other parts of the body and even to other people, sometimes causing infection. In individuals whose immune systems are damaged—burn victims, leukemia or AIDS patients—this could be lethal.
Paoletti admits that his newly engineered vaccines may not be for everyone, but believes that with a little restructuring they could be improved. "We may be able to delete genes that are responsible for the undesirable side effects of vaccinia," he says. In short, the techniques of genetic alchemy that made the vaccines possible could ultimately be used to make them safer.